Age-related differences in the persistence of immunity to varicella- zoster virus (VZV) were evaluated in 17 adults and 62 children previously immunized with various doses of live atenuated varicella vaccine. Immune response was evaluated by ELISA and VZV-specific lymphocyte stimulation assay. The presence of Th1 and Th2 type cytokines released by T lymphocytes stimulated with VZV was also evaluated. A one year post-vaccination, antibody seropositivity rates were 100% for adults and 94% for children; at five years post- vaccination seropositivity rates were 94% of adults and 95% of children. Cell-mediated immunity to VZV was maintained in 94% of adults and 81% of children at five years post-vaccination. Mean stimulation indices (SI) were significantly higher (p=0.04, Student's t test) at the persistence bleed compared to the one-year bleed in both adults and children. Cytokine responses (IL-2, IL-10 and INF-y) to VZV antigen were equivalent in adults and children. In conclusion, at five years post- vaccination, no differences in the persistence of immunity to VZV were observed in adults versus children as measured by the ELISA, VZV- specific lymphocyte stimulation assay and cytokine production.